(1) Field of the Invention
The present invention relates to a boundary detecting method and apparatus for an automatic working vehicle, and more particularly to a method and apparatus for detecting a boundary between a treated area and an untreated area on the basis of image data provided by an image pickup device for photographing a predetermined range of working area forwardly of the vehicle.
(2) Description of the Prior Art
With the above-noted type of automatic working vehicle such as a lawn tractor or a combine harvester, areas surrounding a working range or area to be treated are manually processed as an already treated area in advance, and the vehicle is caused to treat the untreated area while automatically running along the boundary between the treated area and untreated area. A known method of detecting the boundary utilizes the phenomenon that, when the working is viewed obliquely from above, the untreated area looks dark because of uncut lawn growing therein whereas the treated area looks bright because of light reflected by cut lawn.
According to this method, a predetermined range of the working area forwardly of the moving vehicle is photographed and a variable density image is produced from the photographed image according to its brightness. A transition point is identified in the variable density image where a dense portion changes into a light portion. A group of such transition points is regarded as representing the boundary along which the working vehicle is guided. However, the untreated area locally includes bright spots and similarly the treated area includes dark spots. These spots constitute noise and impede reliable detection of the boundary.
On the other hand, there is a method called HOUGH-transformation as disclosed in U.S. Pat. No. 3,069,654 which, when several points are distributed linearly, forms a straight line on the basis of these points (hereinafter referred to as prospective points). This method will be described briefly with reference to FIG. 13 of the accompanying drawings.
It is well known that, when a point (xi, yi) in the X-Y coordinate system is given, all the straight lines passing therethrough, regardless of the inclination, are expressed in the following equation: EQU .rho.=x.sub.i cos .theta.+Y.sub.i sin .theta.
where .rho. is the length of a vertical line from the origin to the straight line, and .theta. is an angle formed between the vertical line and the X-axis (see FIG. 2(a)). If .rho. and .theta. are fixed to certain values, one straight line passing through the point (x.sub.i, y.sub.i) may be identified.
Since .rho. and .theta. are variables, all the straight lines passing through the point (x.sub.i, y.sub.i) describe one locus curve in .rho.- .theta. plane as shown in FIG. 13(b). This locus is described as in FIG. 12(c) with respect to all prospective points in the X-Y coordinate system. One straight line may be identified by finding the point ( .rho..sub.o , .theta..sub.o ) where the curves representing the loci concentrate, as EQU .rho..sub.o =x.sub.i cos .theta..sub.o +y.sub.i sin .theta..sub.o.
The straight line segment sought is obtained by linking the points on the straight line expressed in the above equation through this operation.
There has been a great technical reluctance in employing this HOUGH-transformation method with the automatic working vehicle for boundary detection since a scattering range is increased unless prospective points are selected properly and a great amount of operation is required for transforming the X-Y plane into the .rho.-.theta. plane.